1. Field of the Invention
The present invention relates to an ink composition, an ink jet recording method and recorded matter, and more particularly to [i] an ink jet composition which is superior in terms of the storability of the recorded matter and superior in terms of discharge reliability, with no clogging of the nozzle when used as an ink jet recording ink, and which makes it possible to obtain high-quality images, [ii] an ink jet recording method, and [iii] recorded matter.
2. Description of the Related Art
Ink jet recording methods are printing methods in which recording is performed by causing small droplets of an ink composition to fly through the air, and causing these droplets to adhere to a recording medium such as paper or the like. Such methods are characterized by the fact that sharp images with a high resolution can be printed at a high speed while using a relatively inexpensive apparatus.
In such ink jet recording methods, recording is performed by discharging liquid droplets of ink from a fine nozzle; these liquid droplets must be continuously and stably discharged from the nozzle.
In recent years, furthermore, there has been an increased demand for the maintenance of high quality over a long period of time, without any deterioration in the recorded image. As a result, various means have been devised for improving the storability of recorded images.
For example, the addition of specified compounds to the recording liquid has been proposed in Japanese Patent Application Laid-Open No. H11-170686 as a method of improving the light resistance of recorded images, and the addition of various other light resistance improving agents has also been proposed, along with novel coloring agents and the like.
Light resistance is improved by many of these methods, and storability is greatly improved in cases where images are stored in a configuration in which the images are cut off from the atmosphere and are exposed only to light, as when images are displayed in frames, albums or the like, so that the image quality can be favorably maintained over a long period of time.
On the other hand, there has been in increase in cases where recorded images are displayed xe2x80x9cas isxe2x80x9d indoors and outdoors in configurations other than the above-mentioned storage configuration, under conditions in which the images come into direct contact with the atmosphere, as in the case of posters, calendars and the like.
In such cases, however, the images are exposed not only to light but also to air; as a result, the problem of a deterioration in the image quality has been encountered. The causes of this deterioration in recorded images are not definitely known; however, it appears that such deterioration results from the effects of various types of oxidizing gases, as typified by ozone and the like, that are present in air.
In particular, in cases where recorded matter is exposed to air for long periods of time, the deterioration of cyan dyes is conspicuous, and the recorded images may show a reddish tinge. Such deterioration of cyan dyes is especially like to occur in cases where recorded matter is stored outdoors.
For example, in Japanese Patent Application Laid-Open No. H7-314882, a method in which the deterioration of recorded images is inhibited by adding compounds selected from a set consisting of thiocyanates and the like to the recording sheet has been proposed as a method for improving the resistance to air (or gases; i.e., [as a method for improving] the gas resistance). In the case of this method, deterioration caused by gases can initially be effectively prevented; however, in cases where the images continue to be exposed to air for a long period of time, the effectiveness of the gas resistance is eventually lost, and an abrupt deterioration begins at the point in time where the effectiveness is lost; as a result, the gas resistance cannot be maintained over a long period of time.
Furthermore, in Japanese Patent Application Laid-Open No. H8-3497, a method in which the gas resistance is improved by adding thiosemicarbazide derivatives, thiocarbohydrazide derivatives or the like to the ink composition has also been proposed. However, there are problems in terms of safety in the case of such additives, so that sufficient verification [of safety] is necessary when these additives are used.
Accordingly, it is an object of the present invention to provide [i] an ink jet composition which is superior in terms of the storability of the recorded matter and superior in terms of discharge reliability, with no clogging of the nozzle when used as an ink jet recording ink, and which makes it possible to obtain high-quality images, [ii] an ink jet recording method, and [iii] recorded matter.
As a result of diligent research, the present inventor discovered that the gas resistance of recorded images can be improved, and the ink discharge reliability can also be improved, by using a construction in which a coloring agent, water, a water-soluble organic solvent and a carbazide type compound and/or hydrazide type compound are included in the ink composition.
The present invention was devised on the basis of the abovementioned findings, and provides an ink composition which contains a coloring agent, water, a water-soluble organic solvent and one or more carbazide type compounds and/or hydrazide type compounds.
It is desirable that the abovementioned organic solvent be a liquid at least in the temperature range of 0 to 40xc2x0 C., that the solubility of this solvent with respect to water at a temperature of 20xc2x0 C. be 1 wt % or greater, and that the saturation vapor pressure of this solvent at a temperature of 20xc2x0 C. be 1.7 Pa or less; furthermore, it is also desirable that the abovementioned organic solvent be contained in the ink composition at the rate of 10 wt % to 35 wt %.
By using the abovementioned construction, it is possible to improve the gas resistance of the recorded images and the discharge reliability of the ink.
In the abovementioned composition, it is desirable that the composition contain one or more solvents selected from a set consisting of glycerol, 1,5-pentanediol and triethylene glycol as the abovementioned organic solvent.
By using the abovementioned construction, it is possible to improve the gas resistance of the recorded images and the discharge reliability of the ink.
Furthermore, in the abovementioned composition, it is desirable that the carbazide type compounds be compounds that are expressed by the general formula R1R2NCONHNR3R4, R1 through R4 each independently indicates a hydrogen atom, an alkyl group which may be substituted, or an aryl group which may be substituted or compounds that are expressed by the general formula R5R6NNHCONHNR7R8, wherein R5 through R8 each independently indicate a hydrogen atom, an alkyl group which may be substituted, or an aryl group which may be substituted. In particular, R3 through R8 are preferably methyl groups.
Furthermore, in the abovementioned composition, it is preferable that the carbazide type compounds be compounds that have two or more carbazide structures in the same molecule.
By using the abovementioned construction, it is possible to improve the gas resistance of the recorded images and the discharge reliability of the ink.
Furthermore, in the abovementioned composition it is desirable that the hydrazide type compounds be compounds that are expressed by the general formula R9CONHNR10R11, wherein R9 through R11 each independently indicate a hydrogen atom, an alkyl group which may be substituted, or an aryl group which may be substituted. In particular, R10 and R11 are preferably methyl groups.
Furthermore, in the abovementioned composition, it is preferable that the hydrazide type compounds be compounds that have two or more hydrazide structures in the same molecule.
Furthermore, from the standpoint of achieving a further improvement in the gas resistance, it is desirable that the abovementioned hydrazide type compounds be contained in the ink composition at the rate of 0.1 wt % to 10 wt %, and a content of 0.5 wt % to 5 wt % is even more desirable.
In cases where the composition contains both carbazide type compounds and hydrazide type compounds, there are no particular restrictions on the ratio of the two types of compounds; however, it is desirable that the total content of both types of compounds be in the range of 0.1 wt % to 10 wt %, and a total content in the range of 0.5 wt % to 5 wt % is even more desirable.
It is even more desirable that the weight ratio of the content of the abovementioned carbazide type compounds and/or hydrazide type compounds to the content of the above-mentioned organic solvent be in the range of 1:3 to 1:100. By using such a construction, it is possible to achieve a further improvement in the gas resistance of the recorded images and the discharge reliability of the ink.
In the ink composition of the present invention, the composition acts especially effectively in cases where dyes consisting of metal complexes are contained in the composition as the abovementioned coloring agent. If dyes consisting of metal complexes are included in the composition, recorded images that have a high image quality and a superior gas resistance can be obtained. Examples of dyes consisting of metal complexes include phthalocyanine dyes, metal complex azo dyes and the like.
In the abovementioned composition, an even more effective action is obtained in cases where dyes consisting of copper complexes are contained in the composition. In particular, recorded images that are even more superior in terms of gas resistance are obtained in cases where copper phthalocyanine dyes are used. Concrete examples of copper phthalocyanine dyes include C. I. Direct Blue 86, 199 and the like.
In the ink composition of the present invention, an especially effective action is also obtained in cases where the composition contains dyes expressed by the following general formula (B) as the abovementioned coloring agent. 
In the above formula, X indicates an anilino group that is substituted by at least one SO3M, Y indicates OH, Cl or a morpholino group, and M indicates H, Li, Na, K, ammonium or an organic amine.
If such dyes are included in the ink composition, recorded images that have a high image quality and a superior gas resistance can be obtained.
Concrete examples of dyes expressed by general formula (B) include the following: 
The abovementioned ink composition may also contain one or more acetylene glycol type compounds. By further including acetylene glycol type compounds in the ink composition, it is possible to increase the discharge stability of the ink without causing any deterioration in the gas resistance of the recorded images.
The abovementioned ink composition may also contain one or more glycol ether type compounds. By using glycol ether type compounds as solvents, it is possible to increase the discharge stability of the ink without causing any deterioration in the gas resistance of the recorded images.
The abovementioned ink composition may also contain one or more humectants consisting of tertiary amines.
Furthermore, the ink jet recording method of the present invention is a method in which recording is performed by discharging liquid droplets of an ink composition and causing the liquid droplets to adhere to a recording medium; this method is characterized in that the abovementioned ink composition is used as the ink composition that is discharged.
By using such a recording method, it is possible to obtain recorded matter that is superior in terms of gas resistance.
Furthermore, as a result of diligent research, the present inventor discovered that the gas resistance of the recorded images can be improved by using a construction in which one or more compounds having the following structure (A) are contained in the ink composition as the abovementioned carbazide type compounds and/or hydrazide type compounds. 
In the above structure (A), R1 and R2 each independently indicate an alkyl group which may be substituted or an aryl group which may be substituted.
By using the abovementioned construction, it is possible to obtain recorded images that are superior in terms of gas resistance.
Furthermore, in the abovementioned composition, it is desirable that R1 and R2 in the compounds having the abovementioned structure (A) be methyl groups.
Furthermore, in the abovementioned composition, it is preferable that the compounds having the abovementioned structure (A) be compounds that have two or more such structures (A) in the same molecule.
By using the abovementioned construction, it is possible to obtain recorded images that are superior in terms of gas resistance.
From the standpoint of improving the gas resistance, it is desirable that the compounds having the above-mentioned structure (A) be contained in the ink composition at the rate of 0.1 wt % to 10 wt %.
A single compound having the abovementioned structure (A) may be added to the ink composition of the present invention, or a mixture of two or more such compounds may be added. In cases where a mixture of such compounds is added, it is desirable that the total content of these compounds in the ink composition be 0.1 wt % to 10 wt %.
In the abovementioned ink composition as well, it is desirable that the composition contain coloring agents of the type described above.
Furthermore, it is desirable that the abovementioned ink composition contain one or more water-soluble organic solvents which are liquids at least in the temperature range of 0 to 40xc2x0 C., and in which the solubility with respect to water at 20xc2x0 C. is 1 wt % or greater, and the saturation vapor pressure at a temperature of 20xc2x0 C. is 1.7 Pa or less. By including specified water-soluble solvents in the ink composition, it is possible to increase the discharge stability of the ink without causing any deterioration in the gas resistance of the recorded images.
In the abovementioned composition, it is desirable that the composition contain one or more solvents selected from a group consisting of glycerol, 1,5 -pentanediol and triethylene glycol as the abovementioned organic solvent.
By using the abovementioned construction, it is possible improve the gas resistance of the recorded images and the discharge reliability of the ink.
From the standpoint of achieving a further improvement in the discharge characteristics, it is desirable that the abovementioned organic solvent(s) be contained in the ink composition at the rate of 10 wt % to 35 wt %.
The abovementioned ink composition may also contain one or more acetylene glycol type compounds. By including acetylene glycol type compounds in the composition, it is possible to increase the discharge stability of the ink without causing any deterioration in the gas resistance of the recorded images.
The abovementioned ink composition may also contain one or more glycol ether type compounds. By using glycol ether type compounds as solvents, it is possible to increase the discharge stability of the ink without causing any deterioration in the gas resistance of the recorded images.
The abovementioned ink composition may also contain one or more humectants consisting of tertiary amines.
Furthermore, the ink jet recording method of the present invention is a method in which recording is performed by discharging liquid droplets of an ink composition and causing the liquid droplets to adhere to a recording medium; this method is characterized in that the abovementioned ink composition is used as the ink composition that is discharged.
By using such a recording method, it is possible to obtain recorded matter that is superior in terms of gas resistance.